1. Field of the Invention
The present invention relates to an apparatus for manufacturing a Group III nitride semiconductor, and particularly to an apparatus for manufacturing a Group III nitride semiconductor according to an Na flux method.
2. Description of the Related Art
Conventionally, an Na flux method for growing a Group III nitride semiconductor crystal is known. According to the Na flux method, sodium (Na) and gallium (Ga) are melted, and a resultant mixed melt is maintained at a temperature of about 800° C. The mixed melt is subjected to reaction with nitrogen under a high pressure of about 100 atmospheres, thereby growing a gallium nitride (GaN) crystal on the surface of a seed crystal.
In order to yield GaN having a low impurity content by the Na flux method, high-purity Na is required. Since Na is highly reactive and highly susceptible to oxidization, weighing and like work are carried out within a glove box filled with an inert gas, such as argon gas. According to a work procedure shown in Japanese Patent Application Laid-Open (kokai) No. 2003-286099, a reaction vessel, which holds a mixed melt of Na and Ga, is separated from an apparatus for manufacturing a Group III nitride semiconductor and is placed in a glove box so as to undergo necessary work. Within the glove box, Ga and Na are placed in a crucible; the crucible is placed in the reaction vessel; and the reaction vessel is closed so as to be sealed from the external atmosphere. Subsequently, the reaction vessel is removed from inside the glove box and is then attached to the manufacturing apparatus.
Japanese Patent Application Laid-Open (kokai) No. 2001-58900 discloses an apparatus for manufacturing a Group III nitride semiconductor according to an Na flux method. The manufacturing apparatus assumes the form of a dual vessel in which a reaction vessel is disposed within a pressure vessel. Such a configuration eliminates the need to employ a reaction vessel having a high withstand pressure, so that costs can be curbed.
In the case where a small-sized reaction vessel is used, a disposable reaction vessel made of stainless steel (SUS) has been used in work as described in Japanese Patent Application Laid-Open (kokai) No. 2003-286099. The disposable type is employed for the need to completely seal the reaction vessel. In the case where a large-sized reaction vessel is used, since such a large-sized reaction vessel made of SUS is expensive, the reaction vessel is required to be reusable. However, since such a reusable reaction vessel cannot be completely sealed, the method of Japanese Patent Application Laid-Open (kokai) No. 2003-286099 involves a drawback in that Na is oxidized before the reaction vessel removed from inside the glove box is attached to the manufacturing apparatus.
It is also possible to dispose the entire manufacturing apparatus within a glove box. However, since a manufacturing apparatus in the form of a dual vessel in which a reaction vessel is disposed within a pressure vessel is large in size, the glove box must be of a large size. This is not economical.